I find that because I overstock a little, I get bashed a lot sometimes. For instance, I was just told I need 120 gallons for 5 goldies and a pair of bristlenose. I feel that my 75, if maintained and filtered properly will support this stock without any issues and I understand that some people like to be extremely conservative in stocking, especially with messy fish with high bioloads like goldfish but that's beside the point.

Personally, I feel as long as you keep up maintenance and provide adequate filtration, as well as don't overstock the tank to the point that the fish don't have room to function, overstocking isn't that big of an issue. I was just curious of other's standpoints. :)

A 120 for 5 goldies is a joke IMO. 5 fancies in a 75 and your still not in heavily stock range IMO. I don't keep goldfish, which I know call for a bit more in regards to stocking. But not that much more, unless you want to keep your upkeep low and water changes to a minimum. For the fish I keep(not goldfish) I tend to average a fish a gallon in many of my tanks. I have 8 GBR in a 40 gallon that holds about 50 fish in total and 6 of those rams are breeding pairs.
Is it bad stocking... no.
Would I tell others to stock like that... no.
Would I complain about others stocking heavier... no.
Thats were the experience and the art comes in. If someone is actually stocked too heavily or with incompatible fish they will experience problems that point towards being overstocked. Until then its really just opinions, experienced or not. Breeders stock like crazy and easily get away with it because they know how and can maintain those tanks fine.

Ah, if you can maintain it, and if there is sufficient space for the fish, it's not as much of a problem. The problem is being able to keep up so the fish don't suffer spikes and bounces in parameters.

I currently have a 55 gallon that's over-stocked on livebearers until I can find homes for some of the youngsters. I think I have thirty-some(ten adults and two sub-adults who are the normal stock), a baby pleco and two three-spot gouramis, and I have two filters, lots of live plants and still have to do regular 30% changes twice a week with smaller 10% ones every three days or so other than that just to keep it stable. Been doing it for about six months without any changes in parameters and spikes, but it's hard work! If you're willing to go to such lengths, it's not so much of an issue.

The other issue is: What KIND of goldfish do you have? If you have the single tailed ones, it's a matter of both space and bioload. If you keep up with maintenance that's good for the bioload, but the space is another matter and you risk stunting and aggression issues, as well as stress from the lack of space which can cause illness. I also don't know about BN plecos with coldwater fish, I thought they liked their water temps in the seventies and goldies typically don't like it past 65 degrees.

Now if you have the smaller type goldies, like the fancy-tails it's another matter, but there are still the same risks with space having five of any kind in tanks smaller than 120 gallons. However, having the ones that stay six to eight inches and under in there, with good proper maintenance and extra filtration, you should be alright. People keep three in a well maintained 55 gallon with no problems provided they keep up with cleaning, a 75 for five fancies should be fine, and doubtful you'll have space issues, but always a thing to watch for.

Over-stocking can be dangerous and isn't usually preferable for experienced keepers, it should be avoided for the fishes sakes, as well as your own back! But if it happens and you put in the hours and work, it's not so bad for some types of over-stocking. =) There is more than one type of it, like people who put a fancy goldfish in a ten gallon and then decide five neon tetras or pygmy cories will fit too. No amount of proper cleaning and maintenance is going to fix that, not only is it too much for the tank to be able to handle even with 90-100% changes daily, but that's the also the wrong kind of fish and the wrong sized tank for the -size- of the fish.

In other words, if you have common goldfish, that's not enough room for them, and a 125 really wouldn't be either. It wont matter how well you care for the tank if it's too small for what you have to grow and swim and socialize properly, see?

I was referring to fancies and goldfish don't need as cold of water as is usually pushed. I plan on keeping the tank 75F. IMO 65 is on the low end for a Goldie even though they can handle colder. I figure once this tank is stocked and the fish have reached adult size I'm looking at 50-60% weekly, maybe a smaller 20-30% inbetween if necessary.

I did not know they could handle temps that high for long periods. =o I've been doing a ton of research on goldfish lately, but I haven't heard that one, honestly. I read that having temps above 72F speeds up their metabolisms and shortens their life-spans by a lot. But, alas! I am still in research mode and have been for...oh, I dunno maybe six months now. I was -thinking- about getting a pair of fancies for my 55 gallon one day, but no time soon likely. Perhaps if I can make a nice amount of pocket money this summer I will buy another large tank and get my pair of fancies. I do so like them. =) Been trying to save for more tanks for a while. lol Or perhaps my long wanted cherry barbs and a few crayfish...or a one more addy. ^_~

I usually do 50% changes weekly sometimes its every 2 weeks if I'm busy. I don't over filter much or not at all IMO. My turnover is 5-7x usually sometimes less depending how clogged things get. The 40 gallon has two sponges maybe 4" cubes or so and thats it.

Each to their own. My 55g is stocked much heavier I don't consider it over stocked. The effort again varies. I use hoses to change water so there is very little work involved. I just try not to drink too much when changing water.

Not gonna mention my stocking when I use to have livebearers, but its the reason I got rid of them all to the first person willing to take them lol...

I don't see anything wrong with 75 for goldies they have a very wide temp range. 65 isn't the lowest either. People overwinter koi and goldfish all the time in minnesota.

Everyones opinion will be different on whats best for fish. I spend $5 at least every 2 weeks on live food for my fish and they certainly don't need that. A lot of time care comes down to preference and what works.

with 2 hw303 sun suns and large water changes (75% or more)weekly.you should be fine.but you have to be on top of those wcs, you are giving yourself no wiggle room.i would use the 304s though.if it were me though i would go without the plecos.this is my personal preference though.i would take no chances with my goldies getting their slime coats sucked off.many people have kept them together with no problem.keep up on the filter maintenance by cleaning one canister every other week.by staggering the upkeep it helps to avoid parameter spikes. keep in mind the type of fancy also.orandas and ryukins get huge.ranchu and telescopes stay a little smaller. make sure that you do not overfeed will be important for water quality.1-2% of their body weight daily will do fine.i suggest keeping the temp between 68-72f.they are not coldwater fish,but rather temperate water fish.this is their "ideal" comfort zone. get a good air pump and bubble stone in there too. the whisper ap series is good for running large bubble walls and deep tanks as well as multiple devices. i have seen breeders keep heavily overstocked tanks with only sponge filters.they are doing 2x weekly water changes at 100%.when i get my ranchu in a few months i will be overstocked.yet i am running a sunsun 303b and a fluval 306 on a 45 gallon.so about the same filtration as you plan on using,but in a tank 30 gallons smaller.i will also upgrade tank size when the time comes.

If you get the tank well started, not just cycled, with all natural bio systems working, have double gph filter capacity and can keep up the water changes you should be fine. Shame on me, I have approximately 70 Endlers in a 30L. They have two sponge filters rated for 125gal, a ex-large corner filter that has carbon so old I just don't remember and duckwwed. I do 20% changes weekly and they are as stable as can be.

The rule is, if you just want a tank to sit in thelivingroom, don't over stock. If you are maintaining tanks to experience fish and their natural behaviors stock away. OOPS, don't try it with cichlids.